New Synthesis of (E)-Allylsilanes with High Enantiopurity via Diastereoselective Intramolecular Bis-Silylation of Chiral Allylic Alcohols

Full text of DOI:10.1021/ja954251x

J. Am. Chem. Soc. 1996, 118, 3061-3062
3061
produced was separated and isolated by column chromatogra-
phy. Treatment of the latter (2) with n-butyllithium in THF at
0 °C led to the formation of 3a in high yield. The transforma-
tion of 2 to 3a may be rationalized by cleavage of the silicon-
oxygen bonds of 2 followed by Peterson-type syn-elimination.8
It is noted that the relative stereochemistry of the three
consecutive stereogenic centers in 2 as well as the trans
geometry of the carbon-carbon double bond in 3a was
completely controlled.
New Synthesis of (E)-Allylsilanes with High
Enantiopurity via Diastereoselective Intramolecular
Bis-Silylation of Chiral Allylic Alcohols
Michinori Suginome, Akira Matsumoto, and Yoshihiko Ito*
Department of Synthetic Chemistry and
Biological Chemistry, Faculty of Engineering
Kyoto UniVersity, Kyoto 606-01, Japan
ReceiVed December 19, 1995
Much interest has been focused on the development of new
and versatile organosilicon reagents which may be utilized for
organic synthesis. Allylsilanes are one of the convenient
organosilicon reagents which have made possible some useful
regio- and stereoselective allylations and [3 + 2] cyclizations.1
Accordingly, the preparation of enantio-enriched allylsilanes is
highly desirable. However, widely applicable synthetic methods
for their preparation are still limited.2-6
It was previously reported by us that intramolecular bis-
silylation of carbon-carbon double bonds was achieved by the
use of a palladium(tert-alkyl isocyanide) catalyst.7 The bis-
silylation reaction with various homoallyl alcohols proceeded
with high regio- and diastereoselectivities, ultimately leading
to the stereoselective synthesis of polyols via oxidative cleavage
of the resultant silicon-carbon bonds.
Herein, we disclose a new synthesis of geometrically pure
(E)-allylsilanes with high enantiopurity by the intramolecular
bis-silylation with chiral (E)- or (Z)-allylic alcohols, which
proceeds with extremely high diastereoselectivity. This highly
enantioselective synthesis of allylsilanes involves stereospecific
1,3-transfer of chirality (eq 1).
The palladium-catalyzed bis-silylation followed by treatment
with n-butyllithium was carried out in one flask without isolation
of 2 to afford allylsilane (E)-3a in 93% yield (Table 1, entry
1).9 The one-pot syntheses of allylsilanes via the bis-silylation
of disilanyl ethers 1b-e bearing various terminal silyl groups
are summarized in Table 1.10 In the case of 1e with the terminal
triisopropylsilyl group, the bis-silylation reaction sluggishly
proceeded under forced conditions (see Table 1) to give only
allylsilane 3e in moderate yield without formation of the
corresponding cyclic siloxane 2 (entry 5). It should be noted
that the (E)-allylsilane 3a was obtained also from (Z)-1a in 83%
yield according to the one-pot procedure with phenyllithium
(eq 3).
Disilanyl ether (E)-1a, which was prepared from the corre-
sponding allylic alcohol and 1-chloro-2,2-dimethyl-1,1,2-tri-
phenyldisilane, was heated for 2 h in the presence of Pd(acac)2
(2 mol %) and 1,1,3,3-tetramethylbutyl isocyanide (8 mol %)
under reflux in toluene (eq 2). The mixture of (E)-allylsilane
3a (49%) and six-membered cyclic siloxane 2 (46%) thus
As we proposed in an earlier paper,7c the intramolecular bis-
silylation may involve a bis(organosilyl)palladium(II) complex
4, which undergoes intramolecular insertion of the carbon-
carbon double bond (eq 4). It is presumed that the insertion
reaction proceeds through the “exo” complex, which is ac-
companied by less steric repulsion than the “endo” one.11
Indeed, the high diastereofacial selection in the intramolecular
bis-silylation led to the stereoselective formation of 2 and (E)-
3. Probably, a four-membered trans-5 initially formed under-
(1) For the stereochemical aspect of the reaction of chiral allylsilanes
with electrophiles, see: (a) Hayashi, T.; Konishi, M.; Kumada, M. J. Am.
Chem. Soc. 1982, 104, 4963-4965. (b) Hayashi, T.; Konishi, M.; Kumada,
M. J. Org. Chem. 1983, 48, 281-282. (c) Masse, C. E.; Panek, J. S. Chem.
ReV. 1995, 95, 1293-1326 and references therein.
(2) Asymmetric cross coupling of R-(silyl)alkyl Grignard reagents with
alkenyl bromides in the presence of chiral ferrocenylphosphine-palladium
complexes: (a) Hayashi, T; Konishi, M.; Ito, H.; Kumada, M. J. Am. Chem.
Soc. 1982, 104, 4962-4963. (b) Hayashi, T.; Konishi, M.; Okamoto, Y.;
Kabeta, K.; Kumada, M. J. Org. Chem. 1986, 51, 3772-3781.
(3) Wittig olefination of enantiomerically enriched R-silylaldehydes:
Bhushan, V.; Lohray, B. B.; Enders, D. Tetrahedron Lett. 1993, 34, 5067-
5070.
(4) Regioselective nucleophilic substitution of enantiomerically enriched
allyl esters and carbamates with (organosilyl)cuprate reagents: (a) Fleming,
I.; Thomas, A. P. J. Chem. Soc., Chem. Commun. 1986, 1456-1457. (b)
Fleming, I.; Higgins, D.; Lawrence, N. J.; Thomas, A. P. J. Chem. Soc.,
Perkin Trans. 1 1992, 3331-3349.
(5) Claisen rearrangement of chiral allylic alcohol derivatives: (a)
Mikami, K.; Maeda, T.; Kishi, N.; Nakai, T. Tetrahedron Lett. 1984, 25,
5151-5154. (b) Sparks, M. A.; Panek, J. S. J. Org. Chem. 1991, 56, 3431-
3438.
(6) Other preparation of enantio-enriched allylic silanes. (a) Buckle, M.
J. C.; Fleming, I.; Gil, S. Tetrahedron Lett. 1992, 33, 4479-4482. (b) Sarkar,
T. K. Synthesis 1990, 969-983, 1101-1111.
(7) (a) Murakami, M.; Andersson, P. G.; Suginome, M.; Ito, Y. J. Am.
Chem. Soc. 1991, 113, 3987-3988. (b) Murakami, M.; Suginome, M.;
Fujimoto, K.; Nakamura, H.; Andersson, P. G.; Ito, Y. J. Am. Chem. Soc.
1993, 115, 6487-6498. (c) Suginome, M.; Matsumoto, A.; Nagata, K.; Ito,
Y. J. Organomet. Chem. 1995, 499, C1-C3. (d) Suginome, M.; Yamamoto,
Y.; Fujii, K.; Ito, Y. J. Am. Chem. Soc. 1995, 117, 9608-9609.
(8) Peterson, D. J. J. Org. Chem. 1968, 33, 780-784.
(9) Prior to the addition of n-BuLi (1.5 equiv) at 0 °C, toluene was
replaced by THF.
(10) The requisite chlorodisilanes were readily prepared by the reaction
of (diethylamino)diphenylsilyllithium with the corresponding triorgano-
chlorosilanes followed by treatment with acetyl chloride. (a) Tamao, K.;
Kawachi, A.; Ito, Y. J. Am. Chem. Soc. 1992, 114, 3989-3990. (b) Tamao,
K.; Kawachi, A.; Nakagawa, Y.; Ito, Y. J. Organomet. Chem. 1994, 473,
29-34.
(11) Tamao, K.; Nakajima, T.; Sumiya, R.; Arai, H.; Higuchi, N.; Ito,
Y. J. Am. Chem. Soc. 1986, 108, 6090-6093. (b) Tamao, K.; Nakagawa,
Y.; Arai, H.; Higuchi, N.; Ito, Y. J. Am. Chem. Soc. 1988, 110, 3712-
3714.
(12) The formation of a trans four-membered ring was observed in the
reaction of the related (2-methyl-3-butenyl)disilane, though the selectivity
was not as high (84:16). See ref 7b.
(13) The disproportionation of siloxetane was described. (a) Barton, T.
J. Pure. Appl. Chem. 1980, 52, 615-624. (b) Bachrach, S. M.; Streitwieser,
A., Jr. J. Am. Chem. Soc. 1985, 107, 1186-1190.
0002-7863/96/1518-3061$12.00/0 © 1996 American Chemical Society

3062 J. Am. Chem. Soc., Vol. 118, No. 12, 1996
Communications to the Editor
Table 2. Synthesis of Enantiomerically Enriched
Table 1. One-Pot Synthesis of Racemic (E)-sec-Allylsilanesa
(E)-sec-Allylsilanes
entry
rac-1
R′′R′2Si
rac-3 (yield/%)b
entry
1 (ee/%)
R1
Me
Me
R2
3 (yield/%)a ee/%b
1
2
3
4
5
(E)-1a
(E)-1b
(E)-1c
(E)-1d
(E)-1e
PhMe2Si
Me3Si
t-BuMe2Si
Et3Si
(E)-3a (93)
(E)-3b (82)
(E)-3c (88)
(E)-3d (92)
(E)-3e (55)
1
2
3
4
5
(R)-(E)-1a (99.7)
(R)-(Z)-1a (96.0)
(S)-(E)-1f (>99.0) Ph
(R)-(E)-1g (99.8)
(R)-(E)-1h (98.2)
n-hex (S)-3a (87)
n-hex (R)-3a (84)
n-hex (S)-3f (95)
97.3
95.4
96.3
98.0
94.8
c-hex n-hex (S)-3g (96)
Me Ph (R)-3h (85)
i-Pr3Si
a Reagents and conditions for entries 1-4: (1) Pd(acac)2 (2 mol %),
1,1,3,3-tetramethylbutyl isocyanide (8 mol %), toluene reflux 2 h; (2)
n-BuLi (1.5 equiv), THF, 0 °C, 0.5 h. For entry 5: Pd(acac)2 (3 mol
%), 1-adamantyl isocyanide (45 mol %), xylene reflux 2 days. b Isolated
yield.
a Isolated yield after treatment with n-BuLi (for entries 1, 3, and 4)
or PhLi (for entries 2 and 5). b Determined by HPLC.
chirality transfer during the transformation of the allylic alcohol
to the corresponding (E)-allylsilane. Thus, (S)-(E)-3a with
97.3% overall ee was obtained from (R)-(E)-1a in 87% yield
by a procedure similar to that used for the synthesis of racemic
allylsilanes (eq 5; Table 2, entry 1).16 The enantiomer, (R)-
(E)-3a, was complementarily synthesized from the (Z)-isomer
with the same absolute configuration (eq 6; entry 2). Reactions
went syn-elimination under the reaction conditions to give (E)-
allylsilane 3 with Ph2SidO, which rapidly reacted, in turn, with
trans-5 to afford siloxane 2.12,13
with some disilanyl ethers of highly enantio-enriched allylic
alcohols (E)-1f-h successfully gave the corresponding allyl-
silanes (E)-3f-h with high enantiopurities in good yields. Thus,
the diastereoselective bis-silylation offers a convenient synthetic
access to (E)-allylsilanes with high enantiomeric purity. The
present method has the advantages of being a general preparation
for highly enantiomerically enriched allylsilanes with complete
selectivity for the (E)-isomer and of having manipulative
simplicity.
The highly selective formation of (E)-allylsilanes prompted
us to use enantio-enriched allylic alcohols, which were readily
available by asymmetric syntheses, e.g., Sharpless kinetic
resolution.14 The palladium-catalyzed reaction of (R)-(E)-1a
(99.7% ee) gave (E)-3a with (S)-configuration (96.1% ee)
together with 2, which was subsequently treated with n-
butyllithium to also give (S)-(E)-3a with 99.1% ee.15 The
mechanism proposed above is in accord with the observed
Supporting Information Available: Detailed experimental pro-
cedures and characterization of the new compounds (5 pages). This
material is contained in many libraries on microfiche, immediately
follows this article in the microfilm version of the journal, can be
ordered from the ACS, and can be downloaded from the Internet; see
any current masthead page for ordering information and Internet access
instructions.
(14) (a) Martin, V. S.; Woodard, S. S.; Katsuki, T.; Yamada, Y.; Ikeda,
M.; Sharpless, K. B. J. Am. Chem. Soc. 1981, 103, 6237-6240. (b) Gao,
Y.; Hanson, R. M.; Klunder, J. M.; Ko, S. Y.; Masamune, H.; Sharpless,
K. B. J. Am. Chem. Soc. 1987, 109, 5765-5780.
(15) Enantiomeric excess was determined by HPLC analysis with a chiral
stationary phase column. The column used is specified in the supporting
information.
(16) For the synthesis of enantio-enriched allylsilanes, palladium catalyst
was removed prior to the treatment with RLi by passing the mixture through
a short column of Florisil.
JA954251X